Chiral anion-mediated asymmetric ring opening of meso-aziridinium and episulfonium ions.
Reactions proceeding through cationic intermediates that lack a Lewis or Brønsted basic site present a challenge for traditional asymmetric catalysis based on chiral metals or organocatalysts. We present an enantioselective ring opening of tetrasubstituted meso-aziridinium ions with alcohol nucleophiles proceeding through a chiral ion pair with a binaphthol-phosphate anion. The reaction is initiated by silver-induced ring closure of beta-chloroamines using the Ag salt of the chiral anion as in situ generated catalyst. Use of insoluble Ag2CO3 as silver source is essential to obtain high enantioselectivity; we believe the chiral phosphate acts as a "chiral anion phase transfer catalyst" to bring silver ion into the organic phase. The chiral anion concept can also be extended to the related asymmetric opening of meso-episulfonium ions generated by protonation of trichloroacetimidates vicinal to sulfides.
Hamilton
Gregory L
GL
Department of Chemistry, University of California, Berkeley, California 94720, USA.
Kanai
Toshio
T
Toste
F Dean
FD
D000838:Anions / Q000737:chemistry; D001388:Aziridines / Q000737:chemistry*; D002254:Carbonates / Q000737:chemistry; D003500:Cyclization; D018030:Silver Compounds / Q000737:chemistry; D013237:Stereoisomerism; D013452:Sulfonium Compounds / Q000737:chemistry*
D000838:Anions; D001388:Aziridines; D002254:Carbonates; D018030:Silver Compounds; D013452:Sulfonium Compounds; C033260:silver carbonate